1. Field of the Invention
The present invention relates to a mask aligner for semiconductor manufacturing alignment and exposure apparatus, and more particularly to a mask aligner having a malfunction disposal device.
2. Description of the Prior Art
It is known that an alignment mark of a mask (original) and that of a wafer (radiation sensitive, such as photosensitive) can be automatically aligned in the field of the alignment and exposure apparatus for manufacturing semiconductor circuits, as disclosed in U.S. Pat. Nos. 4,199,219, 4,251,129 and others. In operation of such automatic alignment devices, it is possible that the automatic operation is disabled by an erroneous detection of the mark, or the like, which may be caused by dust attached to the mask or wafer surface. Heretofore, upon the occurrence of such a malfunction, the machine is stopped as it is, and produces a warning to the operator of the error occurrence.
It is not always assured, however, that the operator is present at the machine whenever the malfunction takes place. So, there may be a time loss from the error occurrence to the arrival of the operator, which can be a serious problem. In the whole surface exposure system which is widely used at present and which exposes the whole surface of the wafer to the pattern of the mask by one shot, the occurrence of disabled alignment prevents the process from proceeding to the next step, so that the loss of time is not completely avoidable. On the contrary, in a TTL alignment step-and-repeat type alignment and exposure apparatus wherein the alignment is effected shot by shot (die by die), the process can go forward as the case may be, despite a malfunction, so that the above loss of time is serious in that it may lead to an avoidable low throughput.